(1) Field of the Invention
The present invention relates to a valve for opening and closing a fluid conduit. More specifically, the present invention relates to apparatus for opening and closing a gas conduit having a generally wide cross sectional area. Although not limited thereto, the invention has utility in a conduit for conducting crude blast furnace gases from a blast furnace used in the manufacture of steel.
(2) Description of the Prior Art
U.S. patent application Ser. No. 909,934, now U.S. Pat. No. 4,253,485 discloses a valve for opening and closing a fluid conduit by means of a shut-off element or valve member having a spherical surface displaceable about its centre of curvature, across a transversal slit in the conduit, between an opening and a closing position.
The shut-off element of the U.S. Pat. No. 4,253,485 essentially consists of a valve member in the form of a spherical cap which, in the closed position, is wedged between a movable seat and a fixed seat of the conduit. In order to ensure adequate hermeticity, the presence of a fluid tight seal at each side of the valve member is indispensible. If one of these seals is incorporated in a peripheral tight joint of the valve member itself it is essential for the second seal to be provided on one of the seats, either the fixed or the movable seat of the conduit, in order to ensure tightness when the valve member is in the open position, i.e. disengaged from the conduit, and the two seats are applied against each other. The fact is that if the two fluid tight joints were mounted on the valve member there would be no seal between the two seats of the conduit.
Unfortunately the seal which has to be provided on one of the facing conduit valve seats, delimiting the slit for the insertion of the valve member, is not easily accessible for removal or replacement of the sealing rings or surfaces. On the other hand, if both joints could be provided on the valve member no problem of accessibility would arise, since in the open position there is no longer any contact between the valve member and the conduit. Unfortunately, however, a valve member such as proposed in the above-mentioned U.S. Pat. No. 4,253,485 does not allow of this possibility.
In a second constructional version, said patent U.S. Pat. No. 4,253,485 proposes a shut-off element of the "goggle valve" type, with a full section and an open section. In this second version it is not necessary to provide a seal on one of the seats which delimit the "flow slit" of the shut-off element.
Unfortunately, the said second constructional version comprising a shut-off element of the goggle valve type is not feasible with the telescopic nature of its supporting arm which enables the full section or the open section to be wedged between the two seatings of the conduit.